Identification and characterization of a novel cold-adapted esterase from a metagenomic library of mountain soil

A novel lipolytic enzyme was isolated from a metagenomic library after demonstration of lipolytic activity on an LB agar plate containing 1% (w/v) tributyrin. A novel esterase gene (estIM1), encoding a lipolytic enzyme (EstIM1), was cloned using a shotgun method from a pFosEstIM1 clone of the metagenomic library, and the enzyme was characterized. The estIM1 gene had an open reading frame (ORF) of 936 base pairs and encoded a protein of 311 amino acids with a molecular mass 34 kDa and a pI value of 4.32. The deduced amino acid sequence was 62% identical to that of an esterase from an uncultured bacterium (ABQ11271). The amino acid sequence indicated that EstIM1 was a member of the family IV of lipolytic enzymes, all of which contain a GDSAG motif shared with similar enzymes of lactic acid microorganisms. EstIM1 was active over a temperature range of 1-50°C, at alkaline pH. The activation energy for hydrolysis of p-nitrophenyl propionate was 1.04 kcal/mol, within a temperature range of 1-40°C. The activity of EstIM1 was about 60% of maximal even at 1°C, suggesting that EstIM1 is efficiently cold-adapted. Further characterization of this cold-adapted enzyme indicated that the esterase may be very valuable in industrial applications.